When Dusk Falls, Fireflies Turn On Their Love Lights

A Close-up Look At Those Friendly Fireflies, Stars Of Summer's Light

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ummer is waning, and fittingly, so are the backyard celebrities of the season, the fireflies.

It's been quite a summer for these insects that charm and do no harm.

Fireflies, or lightning bugs, as some call them, were superabundant this year. Why is hard to say, but scientists suspect that two mild winters allowed greater numbers of the insects to survive to adulthood.

After dusk on a June or July night, the typical back yard -- especially if it had a nice, dark backdrop of woods for contrast -- was aglow with tiny flashes of green. The fireflies are a bit fewer these August nights, but the performance goes on.

What everyone sees is something called biological luminescence, the chemical creation of light by an organism. There are many organisms throughout the world capable of biological luminescence. The kind of light they generate and how they flash it varies widely.

In Brazil, the railroad worm has a red light on its head.

In Thailand, there is a kind of firefly that congregates in great numbers on trees, all flashing on and off at the same time. But the fireflies on one tree will not flash in unison with those on another tree. It must be quite a sight.

The fireflies of New England are more individual. The species we encounter -- and there are several -- mostly fly about within a few feet of the ground, flashing to their own internal rhythm. It seems random, but it isn't.

There is order to it, and purpose -- to mate. Each species has its own flash sequence that the female can identify. The males fly just above the ground, signaling, while the females perch below, often on a blade of grass, watching.

When a female sees a male signal, she signals in return. The pair then exchanges signals back and forth until the male reaches the female, and they mate.

If you take a pocket flashlight and mimic the frequency of the fireflies' signals in your back yard, you can draw the insects to the flashlight. They are perhaps three-quarters-inch long,

yellowish and blackish. They are beetles, actually. They don't bite.

As adults, they eat little, preferring minute particles of plant or insect matter. They present no harm to a garden or lawn.

They are, instead, what William Beebe, the naturalist and author, once called "the lantern bearers," a family of insects that on a summer night "illumine our way like a cloud of tiny meteors."

SOURCES: Scientific American magazine; "The Log of the Sun," by William Beebe; Drs. Mark S. McClure and Robert E.B. Moore, Connecticut Agricultural Experiment Station.